Nuclear magnetic resonance-computed tomography (occasionally referred to as MRI (Magnetic Resonance Imaging) or NMR-CT (Nuclear Magnetic Resonance-Computed Tomography)) is used to obtain tomographic images of a living body by utilizing a nuclear magnetic resonance phenomenon of an atomic nucleus having spin in the living body within the static magnetic field. The aforementioned tomography has features of avoiding radiation exposure as in X-ray CT imaging, being free of influence from the bones, providing high-definition tomographic images along an arbitrary direction, and so on, and therefore, it is used in various medical fields such as surgery and resting (tomographic images obtained by the nuclear magnetic resonance-computed tomography will be hereinafter referred to as MRI images).
For example, the boundary between a brain tumor to be removed in an operation of cranial nerve surgery, and a healthy portion is not clearly recognized in a visual observation manner. Therefore, in the operation of cranial nerve surgery, MRI images of the head region are taken in advance, and an actual operation site are compared with the MRI images of the head region in a repeated manner. Thus, the surgical operation is proceeded while making a diagnosis of the boundary between the brain tumor and the healthy portion. Further, a human's brain includes functionally critical areas (eloquent areas, for example, a pyramidal area, a sensory area, a linguistic area, a visual area, an auditory area, and so on). Thus, distribution of these eloquent areas in what place and in what manner is inspected in advance and the state in which various eloquent areas are distributed is displayed as a map on an MRI image of the head region referred to during the surgery (which map is occasionally referred to as a functional mapping MRI).
In conjunction with the foregoing, the non-patent document 1 discloses an optical surgery navigation apparatus that is constructed in such a manner that in the operation of cranial nerve surgery, an MRI image of the head region taken before surgery, and a space of an operation site are made to correspond to each other using a common coordinate system due to a position detector using infrared light, and the position of a region for which a surgical operation is currently performed is detected and shown on the MRI image.
Further, the non-patent document 2 discloses a navigation apparatus that is constructed in such a manner that ultrasonic tomographic images are picked up by an ultrasonic probe during surgery, and the position of the ultrasonic probe is detected by infrared light, thereby causing an MRI image of the head region taken before surgery to correspond to the ultrasonic tomographic images taken during surgery, and in the same manner as in the optical surgery navigation apparatus as disclosed in the non-patent document 1, an operative region for which the surgical operation is currently performed is shown on the MRI image.
Further, the patent document 1 discloses the technique that the position and orientation of a surgical microscope are detected by an optical position measurement system, data processing of enlargement ratio, focal distance and so on is carried out, and image information such as MRI images of the head region, cerebral images and so on is superimpose-displayed in such a manner as to be aligned with real-time images taken by a surgical microscope during surgery,
Moreover, the patent document 2 discloses the technique that a high-definition MRI image taken before surgery (a preoperative image) is reconfigured into a three-dimensional image, and the three-dimensional image is distorted based on a deformation condition for estimated distortions, and is stored as deformation data, and further, an MRI image is taken during surgery, and a two-dimensional image of an area of interest in the preoperative image is reconfigured into a three-dimensional image, and the similarity to the deformation data is calculated and optimum deformation data is selected, and an image of an object from a calibration mirror is superimpose-displayed thereon.
Patent document 1. JP-A No. 2000-333971
Patent document 2: JP-A No. 2002-102249